A variety of standard methods and devices currently exist for passing electrical signals and current across distinct environments. Such devices are commonly referred to as electrical feedthrus or bulkheads. The intent of electrical feedthrus is to facilitate passage of the electrical signals, current, or both across the distinct environments without breaching the integrity of any boundary between the two distinct environments. One variety of electrical feedthrus includes epoxy encapsulated transmission lines. The transmission lines are usually centered within the epoxy capsule, with the lines running parallel to the epoxy capsule. The epoxy capsule insulates the transmission lines at a boundary between two distinct environments. Another variety of electrical feedthrus includes constructing a boundary body between two distinct environments with non-conductive materials and inserting the transmission lines through the boundary body. The boundary body between the two distinct environments is then sealed by standard sealing techniques, such as the use of an O-ring. Glass and ceramic capsules or boundary bodies are also commonly used.
However, these standard electrical feedthrus have a number of drawbacks. The primary problem associated with standard electrical feedthrus is the use of dissimilar materials for construction of the feedthru. For example, an electrical feedthru (2) shown in FIG. 1 requires a thick pre-formed ceramic or glass insulator capsule (4) set in a body (6) to electrically isolate a pin (8) inserted through the insulator capsule (4) from the body (6). The thick insulator capsule (4) is typically made of glass or ceramic, and the pins (8) and body (6) are metallic. The coefficients of thermal expansion of metals and ceramics are generally quite different. Therefore, to maintain the integrity of the seal between the ceramic and the metal, typical electrical feedthrus are limited to a relatively narrow range of temperatures and pressure fluctuations. For example, if the body (6) is steel and the insulator capsule (4) is ceramic, the body (6) would expand more than twice as much as the insulator capsule (4) when subjected to an increase in temperature. The larger the increase in temperature, the larger the difference between the expansion of the body (6) and the insulator capsule (4). This difference in expansion causes high stresses at an interface (9) between the body (6) and the insulator capsule (4). High stresses at the interface (9) result in feedthrus that are prone to failure, and thus limit the performance of the feedthrough.
Another problem associated with electrical feedthrus is the size. Standard electrical feedthrus are often much too large for many applications, particularly for micro-electro-mechanical-systems (MEMS). The electrical feedthru (2) shown in FIG. 1 is considered a very small one, possibly the smallest currently available ceramic feedthru useful in high pressure, high temperature applications. However, the electrical feedthru (2) shown in FIG. 1 requires a pre-formed ceramic or epoxy insulator capsule (4) that has a wall thickness of at least 750 μm. Further, as the number of transmission lines needed increases, the size of the electrical feedhthrus or bulkheads becomes even larger. Referring again to FIG. 1, only a single pin (8) can be located within the thick insulator capsule (4) while maintaining electrical isolation, and the diameter of the ceramic insulator (4) is at least 2 mm. Therefore, according the spacing shown, it takes at least a diameter of 8.0 mm to arrange the six transmission lines or pins (8). However, in actual practice the electrical feedhtru is at least 9.0 mm in diameter to provide support for the multiple ceramic insulator capsules (4). There are many instances, including applications to MEMS devices, where a much larger density of transmissions lines and a much smaller electrical feedthru would be desirable.
Yet another disadvantage of typical electrical feedthrus is the inability of ceramic, glass, and epoxy material to conduct heat. Poor heat conduction means limited ability to dissipate heat. Therefore, typical electrical feedthrus such as the feedthru (2) shown in FIG. 1 are not capable of efficiently dissipating heat through the body (6). Accordingly, any heat-generating devices connected to the transmission lines (8) must be cooled without the aid of conducting heat through the body (6).